If authority discovery is not enabled, `Overseer` is not enabled,
meaning `NetworkBridge` is not started. Validation/collation protocols
are, however, enabled even if the `NetworkBridge` is not started.

Currently this results in normal Polkadot full nodes advertising these
protocols, accepting inbound substreams and even establishing outbound
substreams for the validation protocol. Since the `NetworkBridge` is
not started and no protocol in Substrate is interested in these
protocol events, the events are relayed to all protocol handlers but
are getting discarded because no installed protocol is interested in them.

Co-authored-by: parity-processbot <>